This application is directed to the fluorination of organic compounds. More specifically, there is disclosed a process for the fluoro-decarboxylation of carboxylic acid compounds.
Attempts to effect the fluorination of organic compounds employing elemental fluorine as the fluorinating agent have resulted in a high degree of fluorolysis and consequently in low yields of desired fluorinated products. Such processes employing solid catalyst masses have proved to be exceedingly cumbersome and difficult to control. One method for fluorinating an organic compound is disclosed in U.S. Pat. No. 2,549,565. This process comprises separately and simultaneously injecting the organic compound and elemental fluorine (gas) into a molten mass consisting of from 20 percent to 70 percent of silver monofluoride and from 80 percent to 30 percent of silver difluoride mainained at a temperature between 200.degree. C. and 500.degree. C.
U.S. Pat. No. 2,702,306 discloses another method of producing organic fluorine compounds. This method consists of reacting halogen fluorides with fluorinatable organic materials, wherein the halogen fluoride is mixed with hydrogen fluoride in concentrations of 10 to 90 percent by weight halogen fluoride and contacting this mixture in the liquid phase with the fluorinatable organic material.
U.S. Pat. No. 3,221,069 discloses a method in which a halogen atom can be introduced into an aromatic compound. This process comprises heating an aromatic carboxylic acid halide at a temperature of from about 200.degree. C. to about 400.degree. C. in the presence of a palladium catalyst.
The production of fluorine-substituted aromatic compounds has been accomplished by utilizing XeF.sub.2 in liquid CCl.sub.4 solution and carrying out the substitution at extremely low temperatures, such as -70.degree. C. After the substitution reaction is complete, the solvent is then removed. Unfortunately, the substitution reaction is quite slow and the reaction equipment is expensive.
Yet another process of producing a fluorine-substituted aromatic compound is disclosed in U.S. Pat. No. 3,833,581. This process comprises the step of reacting certain aromatic compounds in the vapor phase with xenon difluoride vapor at a temperature of about 200.degree. C. and a mole ratio of xenon difluoride to said aromatic compound of no greater than one. Unfortunately, this process requires expensive reaction vessels that can cool the reactants to -78.degree. C.
Halogenated organic compounds have previously been prepared by halo-decarboxylation reactions. In the "Hunsdiecker reaction" the silver salt of a carboxylic acid is reacted with a halogen, which displaces the carboxyl group (see Wilson, C. V., Organic Reactions, 9, 332 [1957]). In another halo-decarboxylation reaction, an ionic halide salt is reacted with a carboxylic acid in the presence of lead tetraacetate (Kochi, J. K., J. Am. Chem. Soc., 87, 2500 [1965]). But these halo-decarboxylation reactions are limited to halogens other than fluorine.